Fusion proteins for use as immunogenic enhancers for inducing antigen-specific t cell responses

ABSTRACT

A vaccine composition comprising a fusion protein for inducing enhanced pathogen antigen-specific T cell responses is disclosed. The fusion protein comprises: (a) an antigen-presenting cell (APC)-binding domain or a CD91 receptor-binding domain, located at the N-terminus of the fusion protein; (b) a translocation peptide of 34-112 amino acid residues in length, comprising an amino acid sequence that is at least 90% identical to SEQ ID NO: 4, 2, 3, or 6, located at the C-terminus of the APC-binding domain or the CD91 receptor-binding domain; and (c) an antigen of a pathogen, located at the C-terminus of the translocation peptide; (d) a nuclear export signal, comprising the amino acid sequence of SEQ ID NO: 13; and (e) an endoplasmic reticulum retention sequence, located at the C-terminus of the fusion protein.

REFERENCE TO RELATED APPLICATION

The present application claims the priority to U.S. ProvisionalApplication Ser. No. 61/733,879, filed Dec. 5, 2012, which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to fusion proteins andimmunology.

BACKGROUND OF THE INVENTION

Molecular biology has enabled the production of subunit vaccines, inwhich the immunogen is a fragment or a subunit of a parent protein orcomplex. The development of a stable vaccine that could elicit T cellsensitizing responses, and be flexible enough to incorporate sequencesfrom many strains of an infectious agent would be desirable.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a fusion protein comprising:

-   -   (a) an antigen-presenting cell (APC)-binding domain or a CD91        receptor-binding domain, located at the N-terminus of the fusion        protein;    -   (b) a translocation peptide of 34-112 amino acid residues in        length, comprising an amino acid sequence that is at least 90%        identical to SEQ ID NO: 4, 2, 3, or 6, located at the C-terminus        of the APC-binding domain or the CD91 receptor-binding domain;        and    -   (c) an antigen of a pathogen, located at the C-terminus of the        translocation peptide;    -   (d) a nuclear export signal, comprising the amino acid sequence        of SEQ ID NO: 13; and    -   (e) an endoplasmic reticulum retention sequence, located at the        C-terminus of the fusion protein.

In one embodiment of the invention, the APC-binding domain or the CD91receptor-binding domain is a polypeptide comprising an amino acidsequence that is at least 90% identical to the sequence selected fromthe group consisting of SEQ ID NOs: 1 and 8-11.

In another embodiment of the invention, the nuclear export signalcomprises the amino acid sequence of SEQ ID NO: 14.

In another embodiment of the invention, the endoplasmic reticulumretention sequence comprises the amino acid sequence of SEQ ID NO: 15.

In another embodiment of the invention, the nuclear export signal islocated between the translocation peptide and the antigen.

In another embodiment of the invention, the nuclear export signal islocated between the antigen and the endoplasmic reticulum retentionsequence.

In another embodiment of the invention, the nuclear export signal andthe ER retention sequence forms a fusion peptide comprising an aminoacid sequence that is at least 90% identical to SEQ ID NO: 12.

In another embodiment of the invention, the translocation peptide has34-61 amino acid residues in length.

In another embodiment of the invention, the translocation peptide has34-46 amino acid residues in length.

In another embodiment of the invention, the APC-binding domain or theCD91 receptor-binding domain is free of the amino acid sequence ofPseudomonas exotoxin A (PE) binding domain I.

In another embodiment of the invention, the APC-binding domain or theCD91 receptor-binding domain comprises the amino acid sequence of SEQ IDNO: 8.

In another embodiment of the invention, the amino acid sequence of theAPC-binding domain or the CD91 receptor-binding domain is SEQ ID NO: 1.

In another embodiment of the invention, the antigen is a fusion antigenof two or more antigenic peptides from a pathogen.

In another embodiment of the invention, the ER retention sequence hasmore than 4 amino acid residues in length.

In another embodiment of the invention, the translocation peptidecomprises an amino acid sequence that is at least 95% identical to SEQID NO: 4, 2, 3, or 6.

In another embodiment of the invention, the APC-binding domain or theCD91 receptor-binding domain exhibits a characteristics of recognizingand binding to a receptor on an antigen-presenting cell (APC) selectedfrom the group consisting of dendritic cells, monocytes. B-cells andlymphocytes.

In another embodiment of the invention, the pathogen is selected fromthe group consisting of PRRSV, PCV, FMDV, CSFV, NDV, Transmissiblegastroenteritis virus (TGEV), Porcine epidemic diarrhea virus (PEDV),Influenza virus. Pseudorabies virus. Prvovirus, Pseudorabies virus,Swine vesicular disease virus (SVDV), Poxvirus, Rotavirus, Mycoplasmapneumonia, Herpes virus, Infectious bronchitis, and Infectious bursaldisease virus.

In another aspect, the invention consists essentially of, or consistingof:

-   -   (a) an antigen-presenting cell (APC)-binding domain or a CD91        receptor-binding domain, located at the N-terminus of the fusion        protein;    -   (b) a translocation peptide of 34-112 amino acid residues in        length, comprising an amino acid sequence that is at least 90%        identical to SEQ ID NO: 4, 2, 3, or 6, located at the C-terminus        of the APC-binding domain or the CD91 receptor-binding domain;        and    -   (c) an antigen of a pathogen, located at the C-terminus of the        translocation peptide;    -   (d) a nuclear export signal, comprising the amino acid sequence        of SEQ ID NO: 13; and    -   (e) an endoplasmic reticulum retention sequence, located at the        C-terminus of the fusion protein.

Further in another aspect, the invention relates to a vaccinecomposition comprising the fusion protein as aforementioned and anadjuvant.

Yet in another aspect, the invention relates to a method for inducingenhanced pathogen antigen-specific T cell responses, comprising:administering a vaccine composition comprising a therapeuticallyeffective amount of the fusion protein of claim 1 to a subject in needthereof, and thereby inducing enhanced pathogen antigen-specific T cellresponses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic drawing showing a full-length Pseudomonasaeruginosa exotoxin A (PE), and partial fragment of PE.

FIGS. 1B-C show vector maps.

FIGS. 2-5 are graphs showing fusion proteins according to the inventioneliciting enhanced CD8⁺/IFN-γ⁺ T cell (FIGS. 2A-5A) and CD4⁺/IFN-γ⁺ Tcell (FIGS. 2B-5B) mediated immunogenicities, respectively.

FIG. 6 shows animal groups, vaccines and dosage used for immunizing theanimals, and immunization schedules.

FIGS. 7-8 are graphs showing tumor size curves and percentage oftumor-free mice in the animal groups vaccinated with various fusionproteins or placebo, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the followingexamples that are intended as illustrative only since numerousmodifications and variations therein will be apparent to those skilledin the art. Various embodiments of the invention are now described indetail. Referring to the drawings, like numbers indicate like componentsthroughout the views. As used in the description herein and throughoutthe claims that follow, the meaning of “a”, “an”, and “the” includesplural reference unless the context clearly dictates otherwise. Also, asused in the description herein and throughout the claims that follow,the meaning of “in” includes “in” and “on” unless the context clearlydictates otherwise. Moreover, titles or subtitles may be used in thespecification for the convenience of a reader, which shall have noinfluence on the scope of the present invention. Additionally, someterms used in this specification are more specifically defined below.

DEFINITIONS

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the invention, and in thespecific context where each term is used. Certain terms that are used todescribe the invention are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitionerregarding the description of the invention. For convenience, certainterms may be highlighted, for example using italics and/or quotationmarks. The use of highlighting has no influence on the scope and meaningof a term; the scope and meaning of a term is the same, in the samecontext, whether or not it is highlighted. It will be appreciated thatsame thing can be said in more than one way. Consequently, alternativelanguage and synonyms may be used for any one or more of the termsdiscussed herein, nor is any special significance to be placed uponwhether or not a term is elaborated or discussed herein. Synonyms forcertain terms are provided. A recital of one or more synonyms does notexclude the use of other synonyms. The use of examples anywhere in thisspecification including examples of any terms discussed herein isillustrative only, and in no way limits the scope and meaning of theinvention or of any exemplified term. Likewise, the invention is notlimited to various embodiments given in this specification.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention pertains. In the case of conflict, thepresent document, including definitions will control.

The term “an antigen-presenting cell (APC) or accessory cell” refers toa cell that displays foreign antigens complexed with majorhistocompatibility complexes (MHC's) on their surfaces. T-cells mayrecognize these complexes using their T-cell receptors (TCRs). Thesecells process antigens and present them to T-cells. Main types ofprofessional antigen-presenting cell are dendritic cells (DCs),macrophages, which are also CD4+ and are therefore also susceptible toinfection by HIV; monocytes, and certain B-cells.

The term “an antigen-presenting cell (APC)-binding domain” refers to adomain (which is a polypeptide) that can bind to an antigen-presentingcell (APC). The APC-binding domain may be a polypeptide comprising anamino acid sequence that is at least 90% identical to the sequenceselected from the group consisting of SEQ ID NOs: 1 and 8-11. AnAPC-binding domain is a ligand that recognizes and binds to a receptoron APC.

Cluster of differentiation 91 (CD91) is a protein that forms a receptorin the membrane of cells and is involved in receptor-mediatedendocytosis.

The term “PE_(t)” refers to a translocation peptide (or a translocationdomain) with 34-112 amino acid residues in length. PE_(t) may comprisesthe amino acid sequence that is at least 90% identical to SEQ ID NO: 2-4and 6. For example, the amino acid sequence of PE_(t) may be a fragmentof a.a. 280-a.a. 313 (SEQ ID NO: 4), a.a. 268-a.a. 313 (SEQ ID NO: 3),aa. 253-a.a. 313 (SEQ ID NO: 2), or a.a. 253-a.a. 364 (SEQ ID NO: 6) ofPE. That is, the amino acid sequence of PE_(t) may contain any region ofthe PE domain II (a.a. 253 to a.a. 364: SEQ ID NO: 6) as long as itcomprises a.a 280-a.a. 313 (SEQ ID NO: 4) essential sequence (i.e., theessential fragment).

The PE₄₀₇ (SEQ ID NO. 7) is described in prior patent (U.S. Pat. No.7,335,361 B2) as PE(ΔIII).

The term “minimum translocation peptide” refers to PE₂₅₃₋₃₁₃ (SEQ ID NO.2), which can translocate an antigen into the cytoplasm of a targetcell.

The term “an endoplasmic reticulum (ER) retention sequence” refers to apeptide whose function is to assist translocation of an antigen from thecytoplasm into ER and retains the antigen in the lumen of the ER. An ERretention sequence comprises the sequence of Lys Asp Glu Leu (KDEL; SEQID NO: 15) or RDEL. An ER retention sequence may comprise the sequenceKDEL, RDEL, KDELKDELKDEL (K3; SEQ ID NO: 16), KKDLRDELKDEL (K3; SEQ IDNO: 17), KKDELRDELKDEL (K3; SEQ ID NO: 18), or KKDELRVELKDEL (K3; SEQ IDNO: 19).

A nuclear export signal (NES) refers to a short amino acid sequence of 4hydrophobic residues in a protein that targets it for export from thecell nucleus to the cytoplasm through the nuclear pore complex usingnuclear transport. The NES is recognized and bound by exportins. Themost common spacing of the hydrophobic residues to beL_(xx)KL_(xx)L_(x)L_(X) (SEQ ID NO. 13), where “L” is leucine, “K” islysine and “x” is any naturally occurring amino acid. For example, anartificial NES may comprise the sequence Leu Gin Lys Lys Leu Glu Glu LeuGlu Leu Ala (LQKKLEELELA; SEQ ID NO: 14).

The term “NESK” refers to a fusion peptide of a NES and an ER retentionsignal (i.e., a NES fused to an ER retention signal). It is anartificial peptide possessing the function of a nuclear export signal(NES) and an ER retention sequence. Thus, it can export an antigen fromthe cell nucleus to the cytoplasm through the nuclear pore complex, andassist translocation of an antigen from the cytoplasm to ER and retainthe antigen in the lumen of the ER. For example, the amino acid sequenceof NESK may be LQKKLEELELAKDEL (SEQ ID NO: 12).

An antigen may be a pathogenic protein, polypeptide or peptide that isresponsible for a disease caused by the pathogen, or is capable ofinducing an immunological response in a host infected by the pathogen,or tumor-associated antigen (TAA) which is a polypeptide specificallyexpressed in tumor cells. The antigen may be selected from a pathogen orcancer cells including, but not limited to, Human Papillomavirus (HPV),Porcine reproductive and respiratory syndrome virus (PRRSV), Humanimmunodeficiency virus-1(HIV-1), Dangue virus, Hepatitis C virus (HCV),Hepatitis B virus (HBV), Porcine Circovirus 2 (PCV2), Classical SwineFever Virus (CSFV), Foot-and-mouth disease virus (FMDV), Newcastledisease virus (NDV), Transmissible gastroenteritis virus (TGEV), Porcineepidemic diarrhea virus (PEDV), Influenza virus. Pseudorabies virus,Prvovirus, Pseudorabies virus, Swine vesicular disease virus (SVDV),Poxvirus, Rotavirus, Mycoplasma pneumonia, Herpes virus, infectiousbronchitis, or infectious bursal disease virus, non-small cell lungcancer, breast carcinoma, melanoma, lymphomas, colon carcinoma,hepatocellular carcinoma and any combination thereof. For example, HPVE7 protein (E7), HCV core protein (HCV core), HBV X protein (HBx) wereselected as antigens for vaccine development. The antigen may be afusion antigen from a fusion of two or more antigens selected from oneor more pathogenic proteins. For example, a fusion antigen of PRRSV ORF6and ORF5 fragments, or a fusion of antigenic proteins from PRRSV andPCV2 pathogens.

The term “treating” or “treatment” refers to administration of aneffective amount of the fusion protein to a subject in need thereof, whohas cancer or infection, or a symptom or predisposition toward such adisease, with the purpose of cure, alleviate, relieve, remedy,ameliorate, or prevent the disease, the symptoms of it, or thepredisposition towards it. Such a subject can be identified by a healthcare professional based on results from any suitable diagnostic method.

The term “an effective amount” refers to the amount of an activecompound that is required to confer a therapeutic effect on the treatedsubject. Effective doses will vary, as recognized by those skilled inthe art, depending on rout of administration, excipient usage, and thepossibility of co-usage with other therapeutic treatment.

The invention relates to fusion proteins for enhancing antigen deliveryand modulating cell-mediated immune response. The fusion proteincomprises: (a) an antigen-presenting cell (APC)-binding domain or a CD91L receptor-binding domain, located at the N-terminus of the fusionprotein; (b) a translocation peptide of 34-112 amino acid residues inlength, comprising an amino acid sequence that is at least 90% identicalto SEQ ID NO: 2-4 and 6 and located at the C-terminus of the APC-bindingdomain or the CD91 receptor-binding domain: and (c) an antigen of apathogen, located at the C-terminus of the translocation peptide; (d) anuclear export signal (NES); and (e) an endoplasmic reticulum (ER)retention sequence, the ER retention sequence being located at theC-terminus of the fusion protein, wherein the NES comprises the aminoacid sequence of SEQ ID NO: 13.

Using the fusion protein PE₃₁₃-ORF2-NESK as an example, the strategy isthat the fusion protein of the invention stimulates the production andactivation of T cells that can recognize the antigen Porcine CircovirusType 2 (PCV2) capsid protein ORF2. The fusion protein comprises, fromN-terminus to C-terminus, a PE domain I (APC-binding domain), atranslocation peptide of 34-112 amino acid residues in length (e.g.,a.a. 253-313 of the PE domain 11), a truncated PCV2 ORF2 protein(N-terminal nuclear localization signal removed), a NES signal and an ERretention sequence (KDEL). The underlying mechanisms of elicitingenhanced ORF2-specific T cell immune responses by PE₃₁₃-ORF2-NESKinvolve the following steps: a) binding to dendritic cell (orantigen-presenting cell) surface receptor (CD91); b) internalization byendocytosis; c) transporting to the ER and proteolytic hydrolysis byfurin in front of the translocation peptide; d) processing andpresenting by MHC 1 complex; and e) activating antigen-specific CD4+ andCD8+ T cells. CD4+ Th1 cells are able to efficiently stimulate andenhance cytotoxic CD8+ T cell immune response. Together, these two armsof the adaptive immune system have the specificity and potency to killPCV2 and PCV2-infected cells.

The fusion protein PE₃₁₃-ORF2-NESK here is distinguishable from thefusion protein vaccine PE₄₀₇-Ag-K3 disclosed by Lai in U.S. Pat. No.7,335,361 in several aspects. Firstly, the length of PE₃₁₃ (SEQ ID NO:5) is 94 amino acid residues shorter than PE₄₀₇(SEQ ID NO: 7), theadvantage of which is that unwanted humoral response elicited by thepresence of an extra fragment of PE is minimized or eliminated.Secondly, the ER retention sequence is shortened. Instead of K3 (thatis, 3 of KDER), only one KDER or RDER is needed. Thirdly, only cytosolicantigen can be processed and presented by MHC type 1 pathway, so theaddition of a NES signal into the fusion protein is beneficial toenhance pathogen antigen-specific T cell responses because increasingthe opportunity of translocation of antigen into cytosol. Antigens of apathogen may be imported into the cell nucleus. By incorporating a NESsignal, the antigen imported into the cell nucleus can be exported tothe cytoplasm by the NES signal of the fusion protein.

EXAMPLES

Without intent to limit the scope of the invention, exemplaryinstruments, apparatus, methods and their related results according tothe embodiments of the present invention are given below. Note thattitles or subtitles may be used in the examples for convenience of areader, which in no way should limit the scope of the invention.Moreover, certain theories are proposed and disclosed herein however, inno way they, whether they are right or wrong, should limit the scope ofthe invention so long as the invention is practiced according to theinvention without regard for any particular theory or scheme of action.

Example 1 Construction of Expression Vectors

FIG. 1A shows PE contains 3 domains (I, II, and III). PE₄₀₇ is theregion from aa. 1 to a.a407 of PE. PE₄₀₇ does not contain the cytotoxicdomain III and thus contains domains I and II. PE₃₁₃ the region from as1 to a.a. 313 of PE. Thus, PE₃₁₃ contains only domain Ia and a partialN-terminal region of domain II of PE.

FIGS. 1B-C show constructions of expression vectors, each of whichcomprises an antigen-presenting cell (APC)-binding domain, atranslocation peptide, an antigen, with (bottom panel) or without (toppanel) a nuclear export signal (NES); and an endoplasmic reticulum (ER)retention sequence (top panel, K3 or bottom panel, K), the ER retentionsequence being located at the C-terminus of the fusion protein. Theplasmids pTac-2-PE₃₁₃-NESK, pTac-2-PE₄₀₇-K3, pTac-2-RAP1-PE₂₆₈₋₃₁₃-NESKand pTac-2-RAP1-PE₂₆₈₋₃₁₃-K3 were generated as follows: The^(NdeI)PE₃₁₃-^((EcoRI, XhoI))-NESK^(XhoI),^(NdeI)PE₄₀₇-^((EcoRI, XhoI))-K3^(XhoI),^(NdeI)RAP1-^((EcoRI))-PE₂₆₈₋₃₁₃-^((EcoRI, XhoI))-NESK^(XhoI) and^(NdeI)RAP1-^((EcoRI))-PE₂₆₈₋₃₁₃-^((EcoRI, XhoI))-K3^(XhoI) fragmentswere synthesized by a PCR method and then ligated into a pUC18 back bondwith kanamycin resistance gene to obtain respective plasmids.

A target DNA encoding an antigen or a fusion antigen of a pathogen ofinterest may then be inserted into the aforementioned plasmids togenerate an expression vector for expression of a fusion protein. Forexample. DNA fragments encoding antigens of Porcine Circovirus Type 2(PCV2) ORF2 (SEQ ID NO: 20), Classical Swine Fever Virus (CSFV) E2 (SEQID NO: 21). Foot-and-mouth disease virus (FMDV) VP1-3A (SEQ ID NO: 24)and Newcastle disease virus (NDV) FHN (SEQ ID NO: 27) were synthesizedand inserted into the plasmids pTac-2-PE₃₁₃-NESK and pTac-2-PE₄₀₇-K3,respectively, to generate the following expression vectors: (1)PE₃₁₃-ORF2-NESK; (2) PE₄₀₇-ORF2-K3; (3) PE₃₁₃-E2-NESK; (4) PE₄₀₇-E2-K3;(5) PE₃₁₃-VP1-3A-NESK; (6) PE₄₀₇-VP1-3A-K3; (7) PE₃₁₃-FHN-NESK; and (8)PE₄₀₇-FHN-K3. DNA fragments encoding antigen of Human PapillomavirusType 16 E7 (SEQ ID NO: 28) were synthesized and inserted into theplasmids pTac-2-PE₄₀₇-K3, pTac-2-RAP1-PE₂₆₈₋₃₁₃-NESK andpTac-2-RAP1-PE₂₆₈₋₃₁₃-K3, respectively, to generate the followingexpression vectors: (9) PE₄₀₇-E7-K3, (10) RAP1-PE₂₆₈₋₃₁₃-E7-NESK and(11) RAP1-PE₂₆₈₋₃₁₃-E7-K3.

Example 2 Protein Expression

E. coli BL21 cells harboring plasmids for expression of fusion proteins(1) PE₃₁₃-ORF2-NESK; (2) PE₄₀₇-ORF2-K3; (3) PE₃₁₃-E2-NESK; (4)PE₄₀₇-E2-K3; (5) PE₃₁₃-VP1-3A-NESK; (6) PE₄₀₇-VP1-3A-K3; (7)PE₃₁₃-FHN-NESK; (8) PE₄₀₇-FHN-K3; (9) PE₄₀₇-K3; (10)RAP1-PE₂₆₈₋₃₁₃-E7-NESK and (11) RAP1-PE₂₆₈₋₃₁₃-E7-K3 were respectivelycultured in Luria Bertani broth containing 25 ppm of kanamycin at 37° C.When the culture reaching early log phase, (A600=0.1 to 0.4),isopropyl-1-thio-β-D-galactopyranoside (IPTG) was added with a finalconcentration of 0.5 to 2 mM for induction. Cells were harvested afterinduction after 4 hours and immediately stored at −70° C. The fusionproteins were purified by urea extraction as described previously (Liaoet al., 1995. Appl. Microbiol. Biotechnol. 43: 498-507) and then wererefolded by dialysis method against 50× volume of TNE buffer (50 mMTris, 50 mM NaCl and 1 mM EDTA) at 4° C. for overnight. The refoldedproteins were subjected to SDS-PAGE analyses and quantitative analysesperformed using Bradford Protein Assay Kit (Pierce). The resultsindicated that most of the refolded proteins were monomers under anon-reduced condition, indicating that the fusion proteins refoldedeasily and were not aggregated.

Example 3 PCV2 Subunit Vaccines Immunogenicity Assay

Mice were vaccinated with 0.1 ml PCV2 subunit vaccine containing 40 μgof PE₃₁₃-ORF2-NESK or PE₄₀₇-ORF2-K3 with aluminum phosphate (a proteinabsorbent for slow release of the fusion protein; 10% v/v) and 10 g ofsaponin (an adjuvant extracted from Quillaja saponaria) via s.c.injection once a week for 3 weeks. The control group (placebo) wasinjected with adjuvant only without the fusion protein. All mice weresacrificed 14 days after the last immunization, and the spleens wereharvested. The splenocytes were isolated and cultured in 6-well plate(10⁸ cells/2 ml/well) with or without the recombinant ORF2 protein inthe presence of 1 μg/ml GolgiPlug (BD Pharmingen, San Diego, Calif.) at37° C. for 16 hr. The stimulated splenocytes were then washed withFACScan buffer and stained with phycoerythrin-conjugated monoclonal ratanti-mouse CD8a and AF700-conjugated monoclonal rat anti-mouse CD4antibodies. Cells were intracellular cytokine stained using theCytofix/Cytoperm kit according to the manufacturer's instructions (BDPharmingen). Intracellular IFN-γ was stained with AF488-conjugated ratanti-mouse IFN-γ to measure the immune response and cytokine levels.Flow cytometry analyses were performed using Gallios flow cytometry withKaluza analysis software (Beckman Coulter).

FIGS. 2A-B show the numbers of CD8 and CD4 positive IFN-γ T cells in thesplenocytes from mice vaccinated with a placebo (adjuvant only withoutthe fusion protein) or fusion proteins, respectively. The IFN-γproduction by CD4+ and CD8+ T cells in splenocytes stimulated with ORF2was detected by intracelluar staining via flow cytometry. Bar graphsshow the numbers of ORF2-specific IFN-γ+ CD4+ T cells (FIG. 2B) andIFN-γ+ CD8+ T cells (FIG. 2A) from each group with (grey bars) orwithout (black bars) stimulation by the ORF2 peptide. The resultsindicated that the mice that had been vaccinated with PE₃₁₃-ORF2-NESKhad more ORF2-specific CD4+ IFN-γ and CD8+ IFN-γ+T cells stimulated bythe ORF2 peptide than the mice that had been vaccinated withPE₄₀₇-ORF2-K3 group.

Example 4 CSFV Subunit Vaccines Immunogenicity Assay

Using the same immunization schedule and dosage, mice were vaccinatedwith CSFV subunit vaccines containing PE₃₁₃-E2-NESK or PE₄₀₇-E2-K3, andsplenocytes isolated, cultured and assayed by a flow cytometry method asdescribed above, except that the recombinant E2 protein was added tostimulate the splenocytes in the culture.

FIGS. 3A-B show the numbers of CD8 and CD4 positive IFN-γ T cells in thesplenocytes from mice vaccinated with a placebo (adjuvant only withoutthe fusion protein) or fusion proteins, respectively. The IFN-γproduction by CD4+ and CD8+ T cells in splenocytes stimulated with E2was detected by intracelluar staining via flow cytometry. Bar graphsshow the numbers of E2-specific IFN-γ+ CD4+ T cells (FIG. 3B) and IFN-γ+CD8+ T cells (FIG. 3A) from each group with (grey bars) or without(black bars) stimulation by the E2 peptide. The results indicated thatthe mice that had been vaccinated with PE₃₁₃-E2-NESK had moreE2-specific CD4+ IFN-γ+ and CD8+ IFN-γ+ T cells stimulated by the E2peptide than the mice that had been vaccinated with PE₄₀₇-E2-K3 group.

Example 5 FMDV Subunit Vaccines Immunogenicity Assay

Using the same immunization schedule and dosage, mice were vaccinatedwith FMDV subunit vaccines containing PE₃₁₃-VP1-3A-NESK orPE₄₀₇-VP1-3A-K3, and splenocytes isolated, cultured and assayed by aflow cytometry method as described above, except that the recombinantVP1-3A protein was added to stimulate the splenocytes in the culture.

FIGS. 4A-B show the numbers of CD8 and CD4 positive IFN-γ T cells in thesplenocytes from mice vaccinated with a placebo or fusion proteins. TheIFN-γ production by CD4+ and CD8+ T cells in splenocytes stimulated withVP1-3A was detected by intracelluar staining via flow cytometry. Bargraphs show the numbers of VP1-3A-specific IFN-γ+ CD4+ T cells (FIG. 4B)and IFN-γ+ CD8+ T cells (FIG. 4A) from each group with (grey bars) orwithout (black bars) stimulation t the VP1-3A peptide. The resultsindicated that the mice that had been vaccinated with PE₃₁₃-VP1-3A-NESKhad more VP1-3A-specific CD4+ IFN-γ+ and CD8+ IFN-γ+ T cells stimulatedby the VP1-3A peptide than the mice that had been vaccinated withPE₄₀₇VP1-3A-K3 group.

Example 6 NDV Subunit Vaccines Immunogenicity Assay

Using the same immunization schedule and dosage, mice were vaccinatedwith FMDV subunit vaccines containing PE₃₁₃-FHN-NESK or PE₄₀₇-FHN-K3,and splenocytes isolated, cultured and assayed by a flow cytometrymethod as described above, except that the recombinant FHN protein wasadded to stimulate the splenocytes in the culture.

FIGS. 5A-B show the numbers of CD8 and CD4 positive IFN-γ T cells in thesplenocytes from mice vaccinated with a placebo or fusion proteins. TheIFN-γ production by CD4+ and CD8+ T cells in splenocytes stimulated withFHN was detected by intracelluar staining via flow cytometry. Bar graphsshow the numbers of FHN-specific IFN-γ+ CD4+ T cells (FIG. 5B) andIFN-γ+ CD8+ T cells (FIG. 5A) from each group with (grey bars) orwithout (black bars) stimulation by the FHN peptide. The resultsindicated that the mice that had been vaccinated with PE₃₁₃-FHN-NESK hadmore FHN specific CD4+ IFN-γ+ and CD8+ IFN-γ+ T cells stimulated by theFHN peptide than the mice that had been vaccinated with PE₄₀₇-FHN-K3group.

Example 7 Enhanced Inhibition of Tumor Growth Induced by Human PapillomaVirus Type 16 E7 Protein

The fusion proteins PE₄₀₇-E7-K3, RAP1-PE₂₆₈₋₃₁₃-E7-K3 andRAP1-PE₂₆₈₋₃₁₃-E7-NESK were expressed and refolded using similar methodsas described above. Mice were challenged with 2×10³ TC-01 cells (mouselung epithelia cell harboring HPV type 16 E7 gene) via s.c. injection toinduce HPV-16 type carcinoma. Twelve days after the TC-01 cellchallenge, mice were vaccinated via s.c. with placebo (PBS), PF₄₀₇-E7-K3(100 mg/dose), RAP1-PE₂₆₈₋₃₁₃-E7-K3 (100 μg/dose) orRAP1-PE₂₆₈₋₃₁₃-E7-NESK (100 μg/dose) with AS04C (GlaxoSmithKline) as anadjuvant once per week for 3 weeks (FIG. 6). AS04C, which is a cytotoxicT lymphocyte-enhancing adjuvant, comprises MPL (monophosphoryl lipid A,an immune potentiator) and aluminum phosphate (a protein absorbent forantigen deliver). The term “K3” refers to an ER retention sequencecomprising KDEL. For example, K3 may be the amino acid sequenceKDELKDELKDEL (SEQ ID NO: 16). The term “NESK” refers to a fusion peptidecomprising a nuclear export signal and an ER retention sequence. In oneembodiment of the invention, the NESK is the amino acid sequenceLQKKLEELELAKDEL (SEQ ID NO: 12). The size of tumors and the number oftumor-free animals in each group were recorded (FIGS. 7 and 8). Thetumor growth was significantly suppressed by vaccines PE₄₀₇-K3,RAP1-PE₂₆₈₋₃₁₃-E7-K3 and RAP1-PE₂₆₈₋₃₁₃-E7-NESK with AS04C as anadjuvant. However, the vaccine RAP1-PE₂₆₈₋₃₁₃-E7-NESK was superior toPE₄₀₇-E7-K3 and better than RAP1-PE₂₆₈₋₃₁₃-E7-K3 in suppressing tumorgrowth and increasing the percentage of tumor-free animals.

Example 8

The following fusion proteins are generated PE₃₁₃-NES-antigen-K,PE₁₋₂₅₂-PE₂₆₈₋₃₁₃-NES-antigen-K, PE₁₋₂₅₂-PE₂₈₀₋₃₁₃-NES-antigen-K. Inaddition, the fragment of PE domain Ia (PE₁₋₂₅₂) of the fusion proteinPE₃₁₃-antigen-NESK is replaced by RAP1 domain 3 (SEQ ID NO: 8). A2Mminimum (SEQ ID NO: 9), HIV-Tat minimum (SEQ ID NO: 10) or HSPs minimum(SEQ ID NO: 11) to generate the fusion proteins RAP1 domain3-PE₂₅₃₋₃₁₃-antigen-NESK, A2M-PE₂₅₃₋₃₁₃-antigen-NESK,Tat-PE₂₅₃₋₃₁₃-antigen-NESK and HSP-PE₂₅₃₋₃₁₃-antigen-NESK, RAP1 domain3-PE₂₆₈₋₃₁₃-antigen-NESK, A2M-PE₂₆₈₋₃₁₃-antigen-NESK,Tat-PE₂₆₈₋₃₁₃-antigen-NESK and HSP-PE₂₆₈₋₃₁₃-antigen-NESK vaccines, RAP1domain 3-PE₂₈₀₋₃₁₃-antigen-NESK, A2M-PE₂₈₀₋₃₁₃-antigen-NESK,Tat-PE₂₈₀₋₃₁₃-antigen-NESK and HSP-PE₂₈₀₋₃₁₃-antigen-NESK, respectively.RAP1 domain 3-PE₂₅₃₋₃₁₃-NES-antigen-K, A2M-PE₂₅₃₋₃₁₃-NES-antigen-K,Tat-PE₂₅₃₋₃₁₃-NES-antigen-K and HSP-PE₂₅₃₋₃₁₃-NES-antigen-K, RAP1 domain3-PE₂₆₈₋₃₁₃-NES-antigen-K. A2M-PE₂₆₈₋₃₁₃-NES-antigen-K,Tat-PE₂₆₈₋₃₁₃-NES-antigen-K and HSP-PE₂₆₈₋₃₁₃-NES-antigen-K vaccines,RAP1 domain 3-PE₂₈₀₋₃₁₃-NES-antigen-K. A2M-PE₂₈₀₋₃₁₃-NES-antigen-K,Tat-PE₂₈₀₋₃₁₃-NES-antigen-K and HSP-PE₂₈₀₋₃₁₃-NES-antigen-K. The cellmediated immune responses enhanced by these vaccines are examined usingsimilar methods as described above.

Table 1 shows SEQ ID NOs. of peptides used for making various fusionproteins.

TABLE 1  Component SEQ ID NO: amino acid residuesMinimum Pseudomonas exotoxin A (PE) binding domain 1 252Ia (APC-binding domain, a.a.1-a.a.252 of PE) PE₂₅₃₋₃₁₃ 2 61PE₂₆₈₋₃₁₃(translocation domain) 3 46PE_(†) Core (PE translocation domain core;  4 34a.a. 280-a.a. 313 of PE) PE₃₁₃ (a.a. 1-a.a. 313 of PE) 5 313 PF₂₅₃₋₃₆₄ 6112 PE₄₀₇ aa. 1-a.a. 407 of PE) 7 407 RAP1 Minimum (domain III of RAP1)8 104 A2M Minimum 9 153 HIV-Tat Minimum 10 24 HSPs Minimum 11 641NESK is LQKKLEELELA KDEL* 12 15NES consensus sequence is L_(XX)KL_(XX)L_(X)L_(X), wherein “L” is 13 11leucine, “K” is lysine and “_(X)” is any naturally occurring amino acid.NES is LQKKLEELELA 14 11 KDEL 15 4 KDELKDELKDEL (K3) 16 12KKDERDELKDEL (K3) 17 12 KKDELRDELKDEL (K3) 18 13 KKDELRVELKDEL (K3) 1913 PCV2 ORF2 (Porcine Circovirus type 2 Open Reading 20 192 Frame 2)CSFV E2 (Classical Swine Fever Virus Envelope 21 328 glycoprotein E2)FMDV VP1 peptide (viral capsid protein a.a. 127-a.a. 22 50 176 of VP1)FMDV 3A peptide (a.a. 21-35 of 3A) 23 15FMDV (Foot-and-Mouth Disease Virus) VP1-3A 24 65 peptide**NDV F peptide (a.a. 65-a.a. 82 of Fusion protein) 25 18NDV HN peptide (a.a. 101-a.a. 111 of Hemagglutinin- 26 11 Neuraminidase)NDV FHN peptide*** 27 29 HPV (Human Papillomavirus) Type16 E7 28 98Full length PE (Exotoxin A. Pseudomonas aeruginosa) 29 613 *The boldletters represents the amino acid sequence of an artificial nuclearexporting signal, the underlined letters represents the amino acidsequence of an endoplasmic reticulum retention signal. **The VP1-3Apeptide is a fusion antigen composed of a.a. 127-aa. 176 of VP1 and a.a.21-a.a. 35 of 3A: i.e., a fusion of FMDV VP1 peptide (SEQ ID NO: 22. andFMDV 3A peptide (SEQ ID NO 23). ***The FHN peptide is a fusion antigencomposed of a.a. 65-a.a. 82 of fusion protein and (a.a. 101 aa. 111 ofHemagglutinin-Neuraminidase, i.e, a fusion of NDV F peptide (SEQ ID NO:25) and NDV HN peptide (SEQ ID NO: 26)

In summary, the results have proved that a fusion protein containing anAPC-binding domain at the N-terminal end, a translocation domain,followed by an antigen of a pathogen, and then a fusion peptide of NESKat the carboxyl terminal end is an improved design over the PE-fusionprotein that is without the fusion peptide of NESK at the carboxylterminus in terms of enhancing cell-mediated immune response,suppressing tumor growth, and/or increasing the percentage of tumor-freeanimals.

While embodiments of the present invention have been illustrated anddescribed, various modifications and improvements can be made by personsskilled in the art. It is intended that the present invention is notlimited to the particular forms as illustrated, and that all themodifications not departing from the spirit and scope of the presentinvention are within the scope as defined in the appended claims.

The embodiments and examples were chosen and described in order toexplain the principles of the invention and their practical applicationso as to enable others skilled in the art to utilize the invention andvarious embodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the foregoing description and the exemplary embodiments describedtherein.

Some references, which may include patents, patent applications andvarious publications, are cited and discussed in the description of thisinvention. The citation and/or discussion of such references is providedmerely to clarify the description of the present invention and is not anadmission that any such reference is “prior art” to the inventiondescribed herein. All references cited and discussed in thisspecification are incorporated herein by reference in their entiretiesand to the same extent as if each reference was individuallyincorporated by reference.

What is claimed is:
 1. A fusion protein comprising: (a) anantigen-presenting cell (APC)-binding domain or a CD91 receptor-bindingdomain, located at the N-terminus of the fusion protein; (b) atranslocation peptide of 34-112 amino acid residues in length,comprising an amino acid sequence that is at least 90% identical to SEQID NO: 4, 2, 3, or 6, located at the C-terminus of the APC-bindingdomain or the CD91 receptor-binding domain; and (c) an antigen of apathogen, located at the C-terminus of the translocation peptide; (d) anuclear export signal, comprising the amino acid sequence of SEQ ID NO:13; and (e) an endoplasmic reticulum retention sequence, located at theC-terminus of the fusion protein.
 2. The fusion protein of claim 1,wherein the APC-binding domain or the CD91 receptor-binding domain is apolypeptide comprising an amino acid sequence that is at least 90%identical to the sequence selected from the group consisting of SEQ IDNOs: 1 and 8-11.
 3. The fusion protein of claim 1, wherein the nuclearexport signal comprises the amino acid sequence of SEQ ID NO:
 14. 4. Thefusion protein of claim 1, wherein the endoplasmic reticulum retentionsequence comprises the amino acid sequence of SEQ ID NO:
 15. 5. Thefusion protein of claim 1, wherein the nuclear export signal is locatedbetween the translocation peptide and the antigen.
 6. The fusion proteinof claim 1, wherein the nuclear export signal is located between theantigen and the endoplasmic reticulum retention sequence.
 7. The fusionprotein of claim 1, wherein the nuclear export signal and the ERretention sequence forms a fusion peptide comprising an amino acidsequence that is at least 90% identical to SEQ ID NO:
 12. 8. The fusionprotein of claim 1, wherein the translocation peptide has 34-61 aminoacid residues in length.
 9. The fusion protein of claim 1, wherein theAPC-binding domain or the CD91 receptor-binding domain is free of theamino acid sequence of Pseudomonas exotoxin A (PE) binding domain I. 10.The fusion protein of claim 9, wherein the APC-binding domain or theCD91 receptor-binding domain comprises the amino acid sequence of SEQ IDNO:
 8. 11. The fusion protein of claim 1, wherein the amino acidsequence of the APC-binding domain or the CD91 receptor-binding domainis SEQ ID NO:
 1. 12. The fusion protein of claim 11, wherein thetranslocation peptide has 34-61 amino acid residues in length.
 13. Thefusion protein of claim 12, wherein the nuclear export signal and the ERretention sequence forms a fusion peptide with an amino acid sequencethat is at least 90% identical to SEQ ID NO:
 12. 14. The fusion proteinof claim 11, wherein the translocation peptide has 34-46 amino acidresidues in length.
 15. The fusion protein of claim 10, wherein thetranslocation peptide has 34-61 amino acid residues in length.
 16. Thefusion protein of claim 15, wherein the nuclear export signal and the ERretention sequence forms a fusion peptide with an amino acid sequencethat is at least 90% identical to SEQ ID NO:
 12. 17. The fusion proteinof claim 1, wherein the antigen is a fusion antigen of two or moreantigenic peptides from a pathogen.
 18. The fusion protein of claim 1,consisting essentially of: (a) an antigen-presenting cell (APC)-bindingdomain or a CD91 receptor-binding domain, located at the N-terminus ofthe fusion protein; (b) a translocation peptide of 34-112 amino acidresidues in length, comprising an amino acid sequence that is at least90% identical to SEQ ID NO: 4, 2, 3, or 6, located at the C-terminus ofthe APC-binding domain or the CD91 receptor-binding domain; and (c) anantigen of a pathogen, located at the C-terminus of the translocationpeptide; (d) a nuclear export signal, comprising the amino acid sequenceof SEQ ID NO: 13; and (e) an endoplasmic reticulum retention sequence,located at the C-terminus of the fusion protein.
 19. A vaccinecomposition comprising the fusion protein of claim 1 and an adjuvant.20. A method for inducing enhanced pathogen antigen-specific T cellresponses, comprising: administering a vaccine composition comprising atherapeutically effective amount of the fusion protein of claim 1 to asubject in need thereof, and thereby inducing enhanced pathogenantigen-specific T cell responses.